A good question. I am referring to you to RFC which is a type of publication from the Internet Engineering Task Force (IETF) and the Internet Society (ISOC), the principal technical development and standards-setting bodies for the Internet.
On April 1998, they have created the publication RFC 2328 for OSPF version 2, and on point 9.5 they spoke about “Sending Hello Packets” as following:

“Hello packets are sent out each functioning router interface. They are used to discover and maintain neighbor relationships.[6] On broadcast and NBMA networks, He

sir
1> you have this command ip ospf dead-interval minimal hello-multiplier 3 why you have used 3 what is the meaning of minimal hello-multiplier 3 , I understand that when we select minimal the =n our dead interval time will be 1 but why you used hello-multiplier 3 please explain it but if i am using 4 instead of 3 my neighbor adjancecy is working on R1 i have used hello-multiplier 3 and R2 i have used hello-multiplier 4 and they have neighbor adjancency please explain it

The “3” in that command means how many hello packets will be sent in 1 second period. Also when you use that command, that is ip ospf dead-interval minimal hello-multiplier x; The x number or the number of hello packets sent per second doesn’t need to match between the two neighbors.

The main important thing about this feature is for critical environment to be able to detect the loss of neighborship in 1 second.